The invention claims the benefit of Japanese patent application No. HEI 11-083203, filed on Mar. 26, 1999.
1. Field of the Invention
The invention relates to a signal lamp, and more particularly relates to a structure for a traffic signal lamp employing a prescribed reflector for LEDs that has narrow directivity and substantial luminous intensity and which is configured in such a manner that an even light distribution can be attained with relatively few LEDs.
2. Description of the Related Art
FIG. 4 shows an example of a related traffic signal lamp 41. The traffic signal lamp 41 has a lens 42 located at a front surface of the lamp 41 and has a plurality of LEDs 44 on a substrate 43 provided at the rear of the lens 42. When a voltage is applied to the LEDs 44, light from the LEDs 44 is emitted, and the traffic signal lamp 41 functions as a traffic signal. A housing covering the substrate is also provided so that rainwater or dust does not enter the substrate on which the LEDs are arranged. The housing and lens are then welded or adhered together (not shown in the drawings).
The LEDs 44 in this type of traffic signal lamp 41 are illuminated as necessary so as to notify drivers of vehicles and pedestrians etc., and the lens may also be given a color or particular design. Information may be communicated, as necessary, using the colors and/or the manner of displaying the light.
As shown in the example in FIG. 5, light is distributed downward from a horizontal line because such a traffic signal lamp is usually provided above the drivers of vehicles, or pedestrians etc. Moreover, the light distribution due to the signal lamp is such that luminous intensity is high just below the horizontal line and falls off as the light proceeds downwards and spreads out over a wide range.
Conventionally, two types of LEDs are used, as shown in FIG. 6. One LED has narrow directivity, and high luminous intensity (FIG. 6a) and the other has wide directivity and low luminous intensity (FIG. 6b). The required light distribution can then be obtained by combining these two types of LEDs as appropriate. There are, however, many cases where the required light distribution cannot be obtained using only LEDs. Therefore, it is necessary to provide prismatic cuts on an outer lens or to provide an inner lens between the LEDs and the outer lens, as shown in FIG. 6(b).
The prismatic cuts at the front surface of the lens are not exactly the same and include, for example, combinations of relatively thick, narrow prismatic cuts 7a for portions which provide a light distribution of a high luminous intensity, and relatively shallow, broad prismatic cuts 7b for portions which provide a light distribution of a low luminous intensity, as shown in FIGS. 7(a)-(d).
However, although the light rays of the LEDs have some amount of directivity, light is also dispersed in a lateral direction due to the shape of the lenses of the LEDs and the shape of the horn on which the LED chips are mounted. Accordingly, only approximately 50% of the light is used in an effective manner. It is therefore necessary to increase the number of LEDs in order to obtain the required amount of light.
Increasing the number of LEDs also increases the amount of heat generated. It is therefore necessary to make the entire traffic signal lamp a certain amount thicker or to provide a heat sink (not shown) at the rear surface of the traffic signal lamp in order to ensure that heat does not accumulate within the traffic signal lamp.
When prismatic cuts are formed in the outer lens or when an inner tens is employed, light attenuation occurs within the lens, with the further inconvenience that the lens itself will become heavier due to being thicker. The combination of relatively deep, narrow prismatic cuts in the high luminous portion of the lens, and the relatively shallow, wide prismatic cuts in the low luminous portion of the lens results in a relatively complex lens.
In summary, only about 50% of light from the LEDs is utilized in related traffic signal lamps, requiring the number of LEDs used to be large. Thus, the conventional LED type lamps are expensive, and the amount of heat output by the LEDs is high, creating a major problem. In addition, the prismatic cuts in a lens placed over the related art signal lamp are often complex, the lamp thickness is often substantial, and the lens is usually relatively heavy.
According to the invention, a signal tamp having a lens at a front surface and an LED mounted on a substrate to the rear of the front lens can comprise a first reflector provided above the LED and extending forward substantially parallel to an optical axis of the LED, and a second reflector provided below the LED, and facing forward and inclined downwards with respect to the optical axis of the LED.
The desired light distribution can therefore be obtained with fewer LEDs by using direct light from LEDs of narrow directivity located at positions where luminous intensity directly below a horizontal line is to be high, and then obtaining reflected light using reflectors that reflect light at a low luminous intensity in a downward direction but which spread light over a wide area.
In accordance with another aspect of the invention, a signal lamp can be provided that includes a housing having a front surface and a back surface, a lens located adjacent the front surface of the housing, an LED located adjacent one of the lens and having housing, and reflector means located adjacent the LED for directing light emitted from the LED towards a predetermined position.
In the invention, it is not necessary to use a complex prismatically cut lens because light distribution is basically performed by the LEDs and reflectors provided in the vicinity of the LEDs.
It is to be understood that both the foregoing detailed description and the following general description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.